Two separate Ni ²⁺ ‐sensitive voltage‐gated Ca ²⁺ channels modulate transretinal signalling in the isolated murine retina

Abstract

PurposeLight-evoked responses from vertebrate retinas were recorded as an electroretinogram (ERG). The b-wave is the most prominent component of the ERG, and in the bovine retina its NiCl2-sensitive component was attributed to reciprocal signalling by pharmacoresistant R-type voltage-gated Ca2+ channels, which similar to other voltage-dependent Ca2+ channels trigger and control neurotransmitter release. The murine retina has the great advantage that the effect of gene inactivation for Ni2+-sensitive Ca2+ channels can be analysed to prove or disprove that any of these Ca2+ channels is involved in retinal signalling.MethodsSuperfused retinas from different murine genotypes lacking either one or both highly Ni2+-sensitive voltage-gated Ca2+ channels were used to record their ex vivo ERGs.ResultsThe isolated retinas from mice lacking Cav2.3 R-type or Cav3.2 T-type or both voltage-gated Ca2+ channels were superfused with a NiCl2 (15 μm) containing nutrient solution. The change in the b-wave amplitude and implicit time, caused by NiCl2, was calculated as a difference spectrum and compared to data from control animals. From the results, it can be deduced that Cav2.3 contributes rather to a later component in the b-wave response, while in the absence of Cav3.2 the gain of Ni2+-mediated increase in the b-wave amplitude is significantly increased, probably due to a loss of reciprocal inhibition to photoreceptors. Thus, each of the Ni2+-sensitive Ca2+ channels contributes to specific features of the b-wave response.ConclusionBoth high-affinity Ni2+-sensitive Ca2+ channels contribute to transretinal signalling. Based on the results from the double knockout mice, additional targets for NiCl2 must contribute to transretinal signalling, which will be most important for the structurally similar physiologically more important heavy metal cation Zn2+.

Ca_v2.3 Ca²⁺ Channel Interacts with the G1-subunit of V-ATPase

“…Further, the retinas from Ca v 2.3-deficient mice loose partially the NiCl 2 -mediated effects [38], indicating that Ca v 2.3 contributes partially to transretinal signalling.…”

Electroretinographic Recordings from the Isolated and Superfused Murine Retina

“…The ERG traces before and after NiCl 2 superfusion indicate that during this period b-wave gets maximally increased (Fig. 7), as reported recently [9]. To test the stability of the isolated murine retina for its transretinal signalling capability (Fig.…”

“…After changes for the retina isolation as well as for the recording conditions, a full ERG was obtained, which even could be subdivided for the b-wave response into at least two different fractions [9]. Finally, two important topics will be covered for successful ERG recordings.…”

“…The superimposed traces in Fig. 3B reveal that over time (60 -215 min) the amplitude did not decrease much, but the implicit time got shorter and the shape of the b-wave changed indicating that the transretinal signalling varied (compare to later results with the different mouse mutants, especially the ERGs from Ca v 2.3-deficient mice, which are lacking the later fraction of the b-wave [9]). The major goal for murine ERG-recording was the demonstration of an increase of the bwave amplitude after the superfusion of low NiCl 2 (10 -30 µM).…”

Selected aspects of retinal signaling and energy metabolism and its perspective as a cerebral surrogate model

“…Low concentrations (10 and 30 µM) augmented the b-wave amplitude while higher concentrations (100 µM) inhibited the b-wave amplitude reversibly. Starting from this observation, our group repeated the experiments for the bovine [52] and the murine retina [53]. Isolated murine retinas from control mice and from Ca v 2.3-deficient (as well as from Cav3.2/T-type-deficient) channels were compared for their response to 15 µM NiCl 2 .…”